feat: PrismFacet core implementation

- Plugin scaffold: manifest, tsconfig, package.json
- Router loader with dynamic import + cache busting for hot reload
- Rule store: CRUD on rules.json
- Prompt injector: resolve routers → match rules → read files → inject
- MCP tool: prompt_rules (add/remove/list/test/reload-routers/list-routers)
- Built-in routers: agent-id (zero-dep), role, position (ego.json)
- before_prompt_build hook for system prompt injection

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openclaw.plugin.json

@@ -0,0 +1,20 @@
+{
+  "id": "prism-facet",
+  "name": "PrismFacet",
+  "version": "0.1.0",
+  "description": "Dynamic system prompt injection via routers and rules",
+  "main": "dist/index.js",
+  "configSchema": {
+    "type": "object",
+    "properties": {
+      "routersDir": {
+        "type": "string",
+        "description": "Directory containing router .ts/.js files (default: {pluginDir}/routers)"
+      },
+      "rulesFile": {
+        "type": "string",
+        "description": "Path to rules.json (default: {pluginDir}/rules.json)"
+      }
+    }
+  }
+}